1. Field of the Invention
The present invention relates to a thermosensitive recording material which utilizes the color which forms as a result of the chemical reaction of a coloring agent, such as an electron donor, with a coloring developer, such as an electron acceptor, and more particularly to an improved transparent thermosensitive recording material, having excellent transparency and printing qualities which is used, for example, as a block copy sheet in gravure printing, offset printing and screen printing, as a transparent document sheet for OHP (over head projection), and as a transparent print output sheet for CAD (computer aided design).
2. Discussion of the Background
A thermosensitive recording material is well known in which a colored image is formed by the chemical reaction of a coloring agent, such as an electron donor, with a coloring developer, such as an electron acceptor, wherein color formation is induced when the coloring agent is subjected to heat and/or pressure, or the like.
The thermosensitive recording material has the following advantages over other conventional recording media;
(1) color images can be rapidly recorded by a relatively simple apparatus without the use of such complicated steps as development and fixing;
(2) color images can be recorded without producing noise and environmental pollution;
(3) various color images, for example, red, blue, violet and black, can be easily obtained;
(4) image density and background whiteness are high; and
(5) the manufacturing cost is low.
Because of these advantages, the above described type of thermosensitive recording material can be widely used, not only as a recording material for price labels in stores, but also for copying documents and as print outputs for computers, facsimiles, automatic vending machines of labels and tickets, video printers and measuring instruments.
Recently, as the demand for thermosensitive recording materials continues to grow, thermosensitive recording materials are required to be useful for the document sheets for OHP, original sheets for diazo process reprography, print output sheets for CAD, and block copy sheets for gravure printing, offset printing and screen printing. In order to be useful in these areas, an improved thermosensitive recording material is desirable which has excellent transparency and print quality, which includes dimensional accuracy of a printed image. Japanese Laid-Open Pat. Applications Nos. 61-121875, 1-99873 and 64-90788 disclose transparent thermosensitive recording materials.
However, the known transparent thermosensitive recording materials have several shortcomings which include:
(1) the transparency of the materials is not sufficient to permit checking of several superimposed drawings printed on sheets of the transparent thermosensitive recording material; and
(2) production costs are relatively expensive because of the complicated production process required in which a coating liquid for a thermosensitive coloring layer is prepared by emulsifying a microencapsuled coloring agent and a coloring developer which is dissolved in a water-insoluble or a hardly water-soluble organic solvent, and coated on a transparent substrate.
In attempting to improve these shortcomings, Japanese Laid-Open Pat. Application No. 5-104859 proposes an improved thermosensitive recording material which has excellent transparency and which is manufactured easily. However, the transparent thermosensitive recording material has shortcomings such as:
(1) the dimensional accuracy of a printed image is not satisfactory because of the slip between the thermosensitive recording material and feeding rollers during printing;
(2) mis-feeding, such as no-feeding or undesirable irregular feeding, of a transparent thermosensitive recording material occurs during printing by a thermal printer using a thermal printhead, because the transparent thermosensitive recording material is electrically charged, for example, by contact with feeding rollers in the thermal printer; and
(3) an undesirable white spot image appears in the printed image, because the transparent thermosensitive recording material, which is charged, attracts dust thereon, and the heat for printing, which is applied by a thermal printhead, cannot be transferred to the thermosensitive coloring layer under or near the dust.
Japanese Laid-open Pat. Application No. 64-90788 discloses a transparent thermosensitive recording material including an antistatic layer. However, the transparent thermosensitive recording material cannot prevent charging of the material, particularly in a low humidity environment.
Because of these reasons, a need exists for a transparent thermosensitive recording material having excellent image quality such as high dimensional accuracy of the printed image, excellent transparency which permits checking of several superimposed drawings printed on the sheets of the transparent thermosensitive recording material, and excellent ability to prevent the charging which causes mis-feeding of sheets during printing and an undesirable which spot in a printed image.